This invention relates generally to a control unit for a resin bed type water softener and more particularly to an improved microcomputer-based control unit for a resin bed water softener which initiates regeneration of the water softener resin bed only when necessary.
The most common type of water softener is the ion exchange resin-type softener having a tank which holds a bed of resin through which the hard water is passed to remove undesirable minerals and other impurities. The capacity of the resin bed to absorb minerals and impurities is finite and it is thus necessary to periodically recharge or regenerate the resin bed with a regenerant, typically a brine solution so as to restore the capacity of the resin bed for further water treatment.
With the earliest types of water softeners regeneration was effected manually only after it was discovered that the treatment capacity of the resin bed has been exceeded and the water flowing therethrough was no longer soft. In an effort to eliminate the need for manual regeneration, water softener control systems were developed utilizing a mechanical clock which initiated water softener regeneration on a periodic basis, the frequency of such regeneration being set in accordance with the known capacity of the resin bed and the anticipated daily usage of soft water. While mechanical clock-type water softener control units have alleviated the need for manually regenerating the water softener resin bed, such water softener control units are subject to the disadvantage that by regenerating the water softener resin bed at fixed intervals, regeneration may actually be occurring too often if actual soft water consumption is less than the anticipated soft water consumption or not often enough when the actual soft water consumption exceeds the anticipated soft water consumption. Regenerating the water softener resin bed when sufficient capacity still exists to treat an amount of water equal to, or in excess of the anticipated soft water consumption, is wasteful of salt and the water needed in regeneration. Conversely, failure to regenerate the water softener resin bed after the resin bed capacity has diminished to a point below that required to treat the actual quantity of soft water demanded results in hard water leaving the water softener.
In an effort to better regulate the frequency of water softener resin bed regeneration, demand-type water softener control units have been developed which sense the remaining capacity of the water softener resin bed to soften water. Most present day demand-type water softener control units operate to initiate regeneration of the water softener resin bed at an off-peak time, usually 2:00 a.m., if the remaining capacity of the water softener resin bed, as sensed by the control, is less than that required to refine the amount of water which would likely be used prior to the next regeneration interval. While demand-type water softener control units do achieve better regulation of water softener resin bed regeneration than do mechanical clock-type water softener control units, the frequency at which such demand-type water softener control units initiate regeneration is dependent on the selected reserve value representing the anticipated amount of soft water which will be used prior to the next regeneration interval. Since the actual amount of soft water used will likely not remain constant, but will vary greatly from day to day, the chosen reserve value must be made large to assure that soft water will always be produced by the water softener. Thus, regeneration will likely occur at a greater frequency than is actually necessary.
In an effort to overcome the disadvantages of prior art water softener control units, I previously invented the "Microcomputer Controlled Demand/Scheduled Water Softener" described and claimed in copending U.S. patent application Ser. No. 412,279 filed Aug. 27, 1982, now U.S. Pat. No. 4,426,294 and assigned to the assignee of the present invention. The water softener described in that patent application operates to initiate water softener regeneration when a reserve value, calculated in accordance with the average daily soft water consumption, exceeds the remaining treatment capacity of the water softener. The remaining treatment capacity of the water softener resin bed is mathematically calculated by first determining the total treating capacity of the water softener resin bed, in accordance with the ratio of the unit's softening capacity (as measured in kilograins) to the incoming water hardness (as measured in grains/gallon). The remaining capacity is then obtained from the difference between the total resin bed softening capacity (in gallons) and the quantity of water used since the previous regeneration.
The calculation of the remaining water softener resin bed capacity performed by the control of my previous invention assumes that the hardness of the water remains constant and that the total treating capacity of the water softener resin bed also remains constant. However, in practice the hardness of the water entering the water softener frequently varies for many reasons. Additionally, the treating capacity of the water softener resin bed itself may vary from the specified treating capacity because the treating capacity of the resin itself may vary from that specified by the manufacturer. Furthermore the amount of salt used for each regeneration may vary because of inaccuracies in the control operation. This will cause the capacity of the resin to vary proportionately. Also, the resin bed volume may not be accurately known so that the calculated remaining water softener resin bed capacity may not always equal the actual remaining water softener resin bed capacity.
In an effort to overcome these possible deficiencies, the present invention concerns an improved microcomputer-based water softener control unit which includes a resin bed sensor for sensing when approximately one-half, or any other portion, of the resin bed treating capacity has been depleted. Information from the resin bed sensor indicative of a predetermined depletion of the total resin bed refining capacity is processed by the microcomputer together with data indicative of the measured volume of the soft water consumed to yield a value, as measured in gallons, of the total resin bed capacity that results from the previous regeneration. This affords a much more accurate manner of determining the actual resin bed capacity than calculating the resin bed capacity using a theoretical value of the bed capacity and a single value of the water hardness. At a given time each day the microcomputer-based control system initiates water softer regeneration if a reserve value, calculated in accordance with the actual soft water consumption exceeds the remaining water softener resin bed capacity as previously determined from the resin sensor information and the measured value of soft water consumed.